Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous compounds, which may include nitrogen oxides, and solid particulate matter, which may include unburned hydrocarbon particulates called soot.
Due to increased attention on the environment, exhaust emission standards have become more stringent. The amount of air pollutants emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of particulate matter exhausted to the environment has been to develop new engines, which dynamically tailor the compression ratio of the engine to reduce exhaust emissions while allowing for efficient operation of the engine under a range of conditions.
One example of dynamically changing the compression ratio of an engine is described in U.S. Pat. No. 6,247,430 (the '430 patent), issued to Yapici on Jun. 19, 2001. The '430 patent describes an internal combustion engine having a compression ratio setting device with a plurality of eccentric rings surrounding a crankshaft. The compression ratio setting device also includes two-piece ring-supporting bearing housings that are supported within the cylinder block of the engine. The compression ratio setting device further includes a single centralized ring turning assembly that adjusts the angular position of the eccentric rings relative to the ring-supporting bearing housings to radially shift the crankshaft, whereby an upper dead center position of pistons connected to the crankshaft is altered for varying the compression ratio of the internal combustion engine.
Although the compression ratio setting device of the '430 patent may alter the compression ratio of the internal combustion engine, it may be complex and may have insufficient strength for high power density applications. In particular, because the single centralized ring supporting housing is two piece, additional parts, manufacturing processes, and assembly processes may be required to produce an engine incorporating the compression ratio setting device of the '430 patent. Further, because the ring supporting housing is two piece, the ring supporting housing may be less adequate to resist high power density loading than if the ring supporting housing were a single integral piece.
In addition, because the compression ratio setting device of the '430 patent utilizes a single centralized ring turning assembly, the design flexibility of the internal combustion engine may be limited. Specifically, the single ring turning assembly is large in order to resist operational loading. The large size of the single ring turning assembly may consume open design space within the engine, thereby limiting the space that may be occupied by neighboring systems or components. Further, because the compression ratio setting device of the '430 patent utilizes a single ring turning assembly, the ring turning assembly must be centrally located to balance loading on the compression ratio setting device. This requirement to centrally locate the ring turning assembly further limits design flexibility of the internal combustion engine employing the compression ratio setting device.
The disclosed variable compression ratio mechanism is directed to overcoming one or more of the problems set forth above.